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//===- EdgeProfiling.cpp - Insert counters for edge profiling -------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass instruments the specified program with counters for edge profiling.
// Edge profiling can give a reasonable approximation of the hot paths through a
// program, and is used for a wide variety of program transformations.
//
// Note that this implementation is very naive. We insert a counter for *every*
// edge in the program, instead of using control flow information to prune the
// number of counters inserted.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "insert-edge-profiling"
#include "ProfilingUtils.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Instrumentation.h"
#include "llvm/ADT/Statistic.h"
#include <set>
using namespace llvm;
STATISTIC(NumEdgesInserted, "The # of edges inserted.");
namespace {
class EdgeProfiler : public ModulePass {
bool runOnModule(Module &M);
public:
static char ID; // Pass identification, replacement for typeid
EdgeProfiler() : ModulePass(&ID) {}
virtual const char *getPassName() const {
return "Edge Profiler";
}
};
}
char EdgeProfiler::ID = 0;
INITIALIZE_PASS(EdgeProfiler, "insert-edge-profiling",
"Insert instrumentation for edge profiling", false, false);
ModulePass *llvm::createEdgeProfilerPass() { return new EdgeProfiler(); }
bool EdgeProfiler::runOnModule(Module &M) {
Function *Main = M.getFunction("main");
if (Main == 0) {
errs() << "WARNING: cannot insert edge profiling into a module"
<< " with no main function!\n";
return false; // No main, no instrumentation!
}
std::set<BasicBlock*> BlocksToInstrument;
unsigned NumEdges = 0;
for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
if (F->isDeclaration()) continue;
// Reserve space for (0,entry) edge.
++NumEdges;
for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
// Keep track of which blocks need to be instrumented. We don't want to
// instrument blocks that are added as the result of breaking critical
// edges!
BlocksToInstrument.insert(BB);
NumEdges += BB->getTerminator()->getNumSuccessors();
}
}
const Type *ATy = ArrayType::get(Type::getInt32Ty(M.getContext()), NumEdges);
GlobalVariable *Counters =
new GlobalVariable(M, ATy, false, GlobalValue::InternalLinkage,
Constant::getNullValue(ATy), "EdgeProfCounters");
NumEdgesInserted = NumEdges;
// Instrument all of the edges...
unsigned i = 0;
for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
if (F->isDeclaration()) continue;
// Create counter for (0,entry) edge.
IncrementCounterInBlock(&F->getEntryBlock(), i++, Counters);
for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
if (BlocksToInstrument.count(BB)) { // Don't instrument inserted blocks
// Okay, we have to add a counter of each outgoing edge. If the
// outgoing edge is not critical don't split it, just insert the counter
// in the source or destination of the edge.
TerminatorInst *TI = BB->getTerminator();
for (unsigned s = 0, e = TI->getNumSuccessors(); s != e; ++s) {
// If the edge is critical, split it.
SplitCriticalEdge(TI, s, this);
// Okay, we are guaranteed that the edge is no longer critical. If we
// only have a single successor, insert the counter in this block,
// otherwise insert it in the successor block.
if (TI->getNumSuccessors() == 1) {
// Insert counter at the start of the block
IncrementCounterInBlock(BB, i++, Counters);
} else {
// Insert counter at the start of the block
IncrementCounterInBlock(TI->getSuccessor(s), i++, Counters);
}
}
}
}
// Add the initialization call to main.
InsertProfilingInitCall(Main, "llvm_start_edge_profiling", Counters);
return true;
}
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